bctagging Lecture 3 Advanced Tagging Concepts Su Dong

b/c-tagging Lecture 3 Advanced Tagging Concepts Su Dong 1

Beginning of lifetime b tag • 1984: Long B lifetime discovered by MAC/MK 2@PEP • 1986: First attempt of lifetime b-tag at TASSO@PETRA with vertex drift chamber • 2 -prong vertex combo weights with event tag efficiencies eb ~18% ec 1. 7% euds 0. 5% Z. Phys C 42 (1989), 17 • Tested b vs light jet properties, • as(b)/as(q)=1. 17+0. 50+0. 28 2

Tagging Signatures 3

b decay signature Bad teaching D B p PV p OK for old detectors with poor resolution PV p Proper perspective (still just one case) 4

B decay vertex zoo 2 vertices ~80%W b e, m, q’ W c c b W D D b 3 vertices ~16% s c s q’ c b W q’ D b b D W q’ n c W c b t D e, m, q’ y W u b 1 vertex <2 % s 5

Vertex Topologies • b->c cascade vertex can often cause a vertex has only 1 track • Tertiary vertex track can naturally have –ve impact parameter signs, especially in 2 D • SLD ZVTOP based tagging framework and ATLAS Jet. Fitter are fully conscious of the cascade vertex structure D+ B p PV p 6

Vertexing Utilities • Most common vertexing tools work on track combinatorial compatibilities. • SLD ZVTOP topological vertexing searches for track overlap density peaks D. J. Jackson, NIM A 388 (1997), 247 There is an ATLAS implementation of ZVTOP 7

Single Track Vertices • ‘Ghost Track’ algorithm was a variant of ZVTOP deployed in the SLD Bs mixing dipole analysis: – https: //arxiv. org/abs/hep-ex/0012043 v 1 • A major feature of the Jet. Fitter b-tag in ATLAS – Giacinto Piacquadio’s thesis – Use b jet direction or existing secondary vertex as virtual b hadron “track” to intersect with additional candidate secondary tracks consistent with the cascade chain. 8

Attach Additional Secondary tracks • Once a seed secondary vertex is found, the picture is sharpened. • Second pass to look for additional tracks consistent with cascade decay along the vertex axis. • 3 D DOCA to vertex axis T<1 mm to remove background • L/D > 0. 3 to pickup compatible tracks 9

Refined NN for Track Attachment • SLD Collab. : PRD 71. 112004, 2005 • Tom Wright Ph. D thesis: SLAC-R 602 (2002) NN output 10

What’s a b jet ? q or Q ? • Z->had LEP/SLD 2. 96+0. 38 0. 254+0. 051 JETSET 1. 36 0. 142 Significant fraction of light jet “mis tag” at SLD 11

Nomenclature • b-tag or B-tag ? • Features generically aiming at b-quark should use “b”. • ”B” is reserved for weakly decaying B mesons only. • One way nomenclature: – – b b b B tag hadron (includes b baryon) fragmentation mixing • Both ways possible depending on context: – B or b mass – B or b lifetime – B or b decay 12

Vertex Mass and Charm Tag 13

PT Corrected Mass • 14

Pt correction mass SLD VXD 2 ATLAS simulation 15

Multivariant 16

Multivariant tag 17

Charm tagging Precision from double tag e 2 b/c separation with vertex mass tag LEP: 4 x 4 MZ vs SLD 0. 5 MZ b contamination in c-tag also calibrated SLD Rb, Rc PRD 71 112004 (2005) 18